Add STM ws_deque tests from multicoretests repo

[jmid]

We now released qcheck-stm so here comes a PR with STM tests of Ws_deque from ocaml-multicore/multicoretests

STM tests are model-based and so describe the intended state of a Ws_deque by a list (type state).
A slight complication is the contract for pop and push which is only allowed by the deque owner.
We therefore use two generators - one for the generator and one for stealers.

From the model description we derive 3 tests:

• a sequential test of push and pop
• a parallel test with one owner and one stealer
• a negative parallel test that breaks the contract and hence fails as expected

[lyrm]

Thanks for the PR ! I have a lot of multicoretests for the lock-free data structures ready and waiting to be added !

[jmid]

Hi @lyrm 👋
Sorry, I didn't notice this was complaining about missing dependencies!
8f0ceb6 adds a hand-written show-function, so ppx_deriving.show is no longer a requirement - but I forgot to remove the (preprocess (pps ppx_deriving.show)) line from the dune rule 🤦
(I don't believe the test from this PR needs ppx_deriving_qcheck)

[lyrm]

Oh, thanks and sorry, I should definitely have seen that !

Note that my initial purpose was just to remove conflicts with the main branch to merge :) Hopefully, it will have done it right this time !